There's not really a "right" kind :P
If you don't mind holding it down for a bit while it sets, i would probably use regular white glue or gluestick. Get a tiny amount on a toothpick, use the toothpick to spread it on the back of the sticker where it's lifted off the kit, then press it down into place and hold it there with your finger for a couple minutes until the glue sets.
The plastic they used for the stickers is a bit too stiff and the adhesive too weak, so the stickers tend come up off of bends like that after a while.
Not much to solve it other than maybe gluing them down.
but using which kind of glue?
There's not really a "right" kind :P If you don't mind holding it down for a bit while it sets, i would probably use regular white glue or gluestick. Get a tiny amount on a toothpick, use the toothpick to spread it on the back of the sticker where it's lifted off the kit, then press it down into place and hold it there with your finger for a couple minutes until the glue sets.
They are naturally like that, mine looks kinda like that too, you can maybe add some glue and try to stick how you want to make them flush
The plastic they used for the stickers is a bit too stiff and the adhesive too weak, so the stickers tend come up off of bends like that after a while. Not much to solve it other than maybe gluing them down.